On September 18 voters in Scotland will go to the polls to decide if the country should remain part of the United Kingdom, or if should become independent.

Mr Darling vowed he would use the next 1 00 days " to bring together most of us in this nation around a common vision of Scotland leading the United Kingdom after September 18, not Scotland leaving the United Kingdom."

He added that pro-Union campaigners were offering what the "overwhelming majority" of Scots want, as Labour, the Conservatives and the Liberal Democrats have all now put forward proposals to devolve more power to Holyrood in the event of a No vote.

Meanwhile Mr Jenkins said: " Over the next 100 days I appeal to every single person who believes in Yes to make it their business to talk with and persuade those who remain undecided to come our way.''

Mr Jenkins was in Edinburgh with Deputy First Minister Nicola Sturgeon to launch Yes Scotland's pledge card, setting out " five very clear guarantees" he said independence would bring.

The Yes campaign has so far g athered 789,191 declarations from people who say they will back independence in the referendum, Mr Jenkins said.

That is just over 200,000 short of the one million target the campaign set when it was first launched.

Yes Scotland also unveiled research showing for every 10 people who have moved from undecided since the autumn, seven have become Yes voters while three have shifted to No.

Mr Jenkins said: " 'I think as people focus in on the vote they are going to have to make in September, more and more they are looking for the clear message of 'what will change?' and 'why will my life be better?' and that's very much what we are trying to get across to people.''

He added: ''I think that the final part of the campaign is going to be about who gets the tone and the mood of the campaign right.

''I think a lot of this will come down to who people trust. Why would people trust David Cameron and George Osborne going forward any more than they have up until now?

''I think the issue of trust will be a big one as we move closer to the vote.''

He dismissed claims that the unionist parties' claims of more powers would boost the No Campaign.

''What people have to be realistic about is what will the appetite be at Westminster seriously to push through further constitutional changes for Scotland after this referendum, and when you've got a very full agenda," the Yes Scotland chief executive said.

The Labour MP argued that the terms of debate had changed as a result of the proposals from the pro-Union parties to devolve more powers.

"It is now clear that a No vote will bring more powers to Scotland within the UK," he said.

"All three of the Scottish parties backing a No vote have put forward broadly similar proposals for further powers."

While he said there is "much that divides us on other issues", he argued that when it came to the constitution, Labour, the Conservatives and the Liberal Democrats are "all now pretty much on the same page".

He stressed the "quiet but resolute majority" had a "crucial role" to play in determining Scotland's future as he called on people to say ''no thanks'' to independence.

Mr Darling said: "I want to use these 100 days not to see Scotland divided further but to bring together most of us in this nation around a common vision of Scotland leading the United Kingdom after September 18, not Scotland leaving the United Kingdom.

''I want to use these 100 days to plan for Scotland's positive, possibility-rich future as part of the United Kingdom and with the substantially enhanced powers for the Scottish Parliament which all three parties have committed to."

Scottish Conservative leader Ruth Davidson said: "I t's imperative in these final weeks of campaigning to offer voters a positive vision of how our nation can progress and have a bigger say within the UK.

"A No vote in September is the patriotic choice to deliver the best of both worlds in Scotland. A No vote ensures more powers for the Scottish Parliament, but still guarantees we can keep the pound."

She pledged: " I will be spending every day of the next 14 weeks arguing passionately for Scotland's place in the UK - it's a future which ensures greater power and responsibility at home, along with greater opportunity and security in the world at large."

But Green MSP Alison Johnstone said: " The Scottish Greens will be using the final 100 days to reach out to everyone concerned about a fairer and greener future, making the case that Scotland can achieve far more with a Yes vote."

She added: "We know though that not all of our supporters are convinced about independence yet, and many are rightly just as critical of the SNP as they are of the parties campaigning for a No vote. This isn't a choice between utopia and disaster, it's simply a chance to take responsibility for ourselves. We believe it's an opportunity we can't afford to miss."